Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment, as examples. A transistor is an element that is utilized extensively in semiconductor devices. There may be millions of transistors on a single integrated circuit (IC), for example. A common type of transistor used in semiconductor device fabrication is a metal oxide semiconductor field effect transistor (MOSFET).
The gate dielectric for MOSFET devices has in the past typically comprised silicon dioxide. However, as devices are scaled down in size, silicon dioxide becomes a problem because of gate leakage current, which can degrade device performance. Therefore, there is a trend in the industry towards the development of the use of high dielectric constant (k) materials (e.g., having a dielectric constant of 3.9 or greater, for example) for use as the gate dielectric in MOSFET devices.
High k gate dielectric development has been identified as one of the grand challenges in the 2003 edition of International Technology Roadmap for Semiconductor (ITRS), incorporated herein by reference, which identifies the technological challenges and needs facing the semiconductor industry over the next 15 years. For low power logic (for portable electronic applications, for example), the main issue is low leakage current, which is necessary in order to extend battery life. Device performance is then maximized according to the low leakage current requirements. Gate leakage current must be controlled in low power applications, as well as sub-threshold leakage, junction leakage, and band-to-band tunneling.
To fully realize the benefits of transistor scaling, the gate oxide thickness needs to be scaled down to less than 2 nm. However, the resulting gate leakage currents make the use of such thin oxides impractical in many device applications where low standby power consumption is required. For this reason, gate oxide dielectric material will eventually be replaced by an alternative dielectric material that has a higher dielectric constant. However, the device performance of using high k dielectric materials suffers from trapped charge in the dielectric layer which deteriorates the mobility, making the drive current lower than in transistors having silicon dioxide gate oxides, and hence reducing the speed and performance of transistors having high k gate dielectric materials.
One proposed method of manufacturing a transistor is to introduce dopants into a top surface of a gate dielectric after depositing a gate dielectric material. See Inumiya, S., et al., “Fabrication of HfSiON Gate Dielectrics by Plasma Oxidation and Nitridation, Optimized for 65 nm node Low Power CMOS Applications,” 2003 Symposium on VLSI Technology Digest of Technical Papers, pp. 18-19, Document No. 4-89114-035-6/03, which is incorporated herein by reference. In this method, nitrogen is introduced on top of a high k gate dielectric using plasma in order to directly nitridize the gate dielectric material. While this method provides increased hole mobility, it requires plasma processes which can be difficult to work with and may cause damage to the devices manufactured, as well as requiring an additional tool for the plasma processing.
Therefore, what is needed in the art is a transistor design and fabrication method having a high k gate dielectric material with increased speed and improved performance, that is compatible with semiconductor device manufacturing processes.